Investigators track two men in Boston Bombing

Updated
Boston Police and Firemen stand by at the scene after explosions interrupted the running of the 117th Boston Marathon in Boston, Massachusetts April 15, 2013.
Boston Police and Firemen stand by at the scene after explosions interrupted the running of the 117th Boston Marathon in Boston, Massachusetts April 15, 2013.
Dominick Reuter/Reuters

Authorities are now seeking two men seen in video near the scene of the Boston Marathon for questioning, officials told NBC News Thursday.

Two bombs went off in quick succession on Monday near the finish line of the Boston Marathon, killing three and injuring nearly 200. Investigators have combed over thousands of tips from the public as well as surveillance video and photographs, looking for clues as to who is responsible for the attack. No one has claimed responsibility, and it is not yet known if it is an act of domestic or international terrorism.

Yesterday, authorities told NBC News they had identified  ”a number of people” who they would like to interview in relation to the bombing but had not made any arrests.

Investigators have said they are focused on those seen carrying black nylon bags and setting them down and walking away near the scene of the explosion. The two bombs are believed to have been contained in metal containers–including one pressure cooker–and filled with shrapnel.

The FBI has given law enforcement agencies a surveillance photo of a man wearing a baseball cap at the scene of the marathon bombing and is asking for help identifying the man, a senior federal law enforcement official who has seen the photo told NBC News Wednesday.

The official who has seen the photo described it as showing a man about six feet tall, wearing a white or off-white baseball cap.

Investigators track two men in Boston Bombing

Updated